Composite structural members are well known in the art. Such structures generally comprise two or more fiber layers made of a high tensile and compressive strength material, such as glass or carbon, encased within a suitable resin matrix and a core material sandwiched between the layers.
Due to the desirable strength to weight ratio, composite members have been employed in a number of applications, including vehicle body modules or panels. Illustrative is the structure disclosed in U.S. Pat. No. 5,042,395.
A major drawback of the noted structure is the undesirable stress concentrations at the panel joints. Indeed, in the structure disclosed in U.S. Pat. No. 5,042,395, the support frame is riveted or screwed to the cover layers at the fitting connections between the body panels.
Referring to FIG. 1, there is shown a cross-sectional view of a conventional structure employing pultruded composite materials connected by a joint 2. The joint, which connects flat preformed panels 4, 6, is typically formed out of aluminum.
In the noted illustration, the preformed panels 4, 6 comprise outer skin portions 4a, 6a, inner skin portions 4b, 6b and core materials 4c, 6c. The preformed panels 4, 6 are attached to the joint 2 by adhesive layers 8 and 10, respectively.
A problem with this type of joint 2 is that it cannot, and will not, adequately protect the structure against the torsion loads, such as that caused by a tractor trailer truck on uneven roads and bumps, or the bending forces caused by loads in the trailer. As illustrated in FIG. 2, when the floor 22 of the trailer 20 is loaded in the direction denoted by Arrow P, the floor 22 deflects downward in the direction denoted by Arrow D, producing tensile forces at the joining edges 23a, 23b of the floor 22 and compressive forces at the joining edges 24a, 24b of the top 21. For this reason, in the conventional trailer construction shown in FIG. 1, the corner joints are made sufficiently stiff so that they carry virtually all the compressive and tension load. The size and resulting stiffness of the corner joint is such that the wall panels provide little contribution to the load carrying structure.
Further, as illustrated in FIG. 1, the bending loads (denoted by Arrow A) at the conventional joint 2 result in undesirable stress concentrations at the skins 4a, 6a of the preformed panels 4, 6 at points 12, 14. The bending loads also urge the panel skins together, crushing the core, or urge the skins apart, causing them to separate from the core material.
Various techniques and/or joint structures have been employed to provide a cost effective and efficient joint for body panels. Illustrative are joints disclosed in U.S. Pat. Nos. 4,662,138; 5,403,063 and 2,934,372. Although each of the noted joints have been deemed acceptable for narrowly defined applications, the resultant stress patterns exhibited by the joints under load is far from optimum.
It is, therefore, an object of the present invention to provide a substantially monocoque joint structure having an optimum stress distribution under load.
It is another object of the present invention to provide a substantially monocoque joint structure which provides a continuous integral load path to joined panels when subjected to conventional loads.
It is another object of the present invention to provide a substantially monocoque joint structure which exhibits a substantially uniform stress profile under conventional loads.
It is yet another object of the present invention to provide a substantially monocoque joint structure which is lightweight, cost effective and efficient.